How to avoid eval when eval seems unavoidable
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Everybody on this forum agrees that eval is a terrible terible thing to use. But often it seems to me to be unavoidable. The one below is only the most recent of these that I have encountered. Suppose I want to "unpack" a struct, using the fields of the struct as variable names.
For example
S.a = 1
S.b = 2
etc
Now I want to create variables a=1 and b=2, etc. The only way I know how to do this goes something like this;
Fields = fieldnames(S);
for ii=1:numel(Fields);
field = Fields{ii};
value = getfield(S,field);
eval([ field '=' num2str(value) ';']);
end
a
b
How can I do a loop like this, without using eval?
2 件のコメント
Steven Lord
2021 年 11 月 1 日
Do you have to unpack the struct? Is there a reason you can't or don't want to just index into the struct?
回答 (2 件)
Matt J
2021 年 11 月 1 日
編集済み: Matt J
2021 年 11 月 1 日
One way to avoid eval in this case is to use an automatic code-writing tool instead of unpacking at run time. I created the following precisely for this purpose,
Walter Roberson
2021 年 11 月 1 日
orderfields, struct2cell, cell expansion in the context of a multiple variable output.
Assuming that the list of fields is fixed but not necessarily their order.
3 件のコメント
Steven Lord
2021 年 11 月 1 日
Why? What's your use case where you need the fields as independent variables?
Walter Roberson
2021 年 11 月 1 日
It is not clear to me why my suggestion is not suitable for your purposes? Do you need to have struct with unpredictable field names that have to be moved into variables?
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